1. Field of the Invention
The invention relates to devices, methods, and programs for estimating light sources, and more particularly to a device, a method and a program for estimating a light source, capable of easily and reliably estimating the light source.
2. Description of the Related Art
In many cases, an image pickup apparatus such as a digital still camera has an automatic white balance function which appropriately controls white balance in accordance with a light source, such as the sun and a fluorescent lamp, during capturing without an instruction of a user. The image pickup apparatus having such a function estimates a light source using a pixel signal obtained through capturing with an image pickup element provided in the image pickup apparatus, and controls the white balance on the basis of a control value appropriate to the estimated light source.
Estimation of a light source during capturing typically uses pixel signals of visible light of the three primary colors, red (R), green (G), and blue (B), obtained through the capturing with the image pickup element. In particular, a value which is obtained using the pixel signals and represents the intensity of the light source is projected in an evaluation space, and then, a black-body radiation locus, predetermined characteristics of the intensity of the light source, and the like, are considered, thereby estimating a light source in a capturing environment.
However, even when light sources in the capturing environment are different, values representing the intensities of the different light sources may be projected in a region in the evaluation space which estimates the light sources as an equivalent light source. It is difficult to accurately estimate the light source. Hence, in order to reliably estimate the light source, suggestions have been made, in which the number of dimensions in the evaluation space is increased, and a new axis is added to the evaluation space to easily discriminate the different light sources.
Also, a method of estimating a light source has been suggested, in which a light source is estimated by using sensors having spectral sensitivities for colors of R, G, and B, and a fourth sensor having a spectral sensitivity for visible light having a longer wavelength than that of R (For example, see Japanese Unexamined Patent Application Publication No. 2004-177395). In this method, with the use of the fourth sensor, the accuracy of the estimation for various types of light sources including a fluorescent lamp can be increased.